1. Field of the Invention
This invention relates to chain-type power transmission belts and, more particularly, to a connection between pulley-engaging tip members and pins which connect a plurality of link plates together to produce an endless, flexible belt configuration.
2. Background Art
It is known to use endless power transmission belts to operate infinitely variable speed changers in the automotive industry. Rubber V-belts, metal chain-type belts and metal belts have all been used for this purpose.
One known type of metal chain-type belt is defined by a plurality of link plates interconnected by pins to define an endless, articulated configuration. V-blocks are interposed between adjacent pins and have tapered surfaces for engagement with cooperating pulleys. Exemplary chain-type power transmission belts of this type are shown in Japanese Patent Application Laid-Open Publication Nos. 57-22442, 59-226729, and 59-226730.
In another known construction for a chain-type power transmission belt, link connecting pins project beyond the side surfaces of the outermost link plates and directly engage cooperating pulley surfaces. The pulleyengaging surfaces of the pins are tapered to conform to the inclination of the engaged pulley surfaces. Exemplary belts of this construction are disclosed in Japanese Utility Model Application Laid-Open Publication No 63-37846. Typically, this type of power transmission belt permits the use of a large diameter pin to provide the required pulley contacting area.
Another known construction for a chain-type power transmission belt is disclosed in Japanese Patent Application Laid-Open Publication No. 63-219937. In this structure, the link-connecting pins project from both sides of the belt. A freely movable tip member is attached to the pin portions that are exposed at the belt sides. The tip members define surfaces to drive and be driven by cooperating pulleys. Preferably, each tip member is connected to be universally movable relative to the pin end. As the tip members engage with and disengage from a pulley, they reorient to keep the pulley-engaging tip member surfaces in substantially facial engagement with the cooperating pulley surface.
This type of belt is desirable, and attempts are being made to commercialize the same, in high load environments. More particularly, the tip members are connected to the pins so as to be universally pivotable relative thereto within a prescribed angular range. As the belt initiates contact with, or separates from, a pulley surface with a high load applied to the belt, the longitudinal and lateral forces applied by the pulley to the tip members reorient the tip members, most commonly by rotation, to cause a facial contact between the tip members and pulley surfaces and thereby distribute impact forces over a substantial surface area.
The face-to-face contact between the pulley surface and tip members prevents noise generation that would otherwise occur with a more localized contact region between the belt and pulley as the tip members are driven against and separated from the pulleys in use. Also, because the tip members reorient, there is no skewing of the belt as might occur with misaligned tip members and pulley surfaces. This avoids the generation of unwanted system vibrations.
This relative movement between the tip members and pins, while accounting for a positive drive characteristic and minimizing noise generation, does introduce a wear problem between parts.
Typically, the tip member is constructed with a spherical opening for reception of a correspondingly configured head of a pin. A tapered surface, converging towards the spherical surface, guides the pin head into the spherical opening during assembly and also avoids interference between the tip member and pin as the tip member reorients. The tapered surface and spherical surface blend together at an edge having a restricted diameter that prevents withdrawal of the spherical head of the pin. It has been found that, over time, repeated pivoting of the tip member in use causes the pin to wear the edge at the juncture of the tapered and spherical surfaces. Excessive wear may allow the pin to fully separate from the tip member with obviously adverse consequences. Even before separation, there may be unwanted play between the pin and tip member due to wear.